In recent years, high integration of semiconductor devices (hereinafter, referred to as “devices”) has been promoted. Meanwhile, when a plurality of highly-integrated devices is connected by wires for production, a problem occurs in that an increase in wire length increases wire resistance and wire delay.
To overcome this problem, the use of a three dimensional integration technique has been proposed which stacks semiconductor devices in three dimensions. In the three dimensional integration technique, for example, a bonding apparatus is used to bond two semiconductor wafers (hereinafter, referred to as “wafers”) together. The boding apparatus includes, for example, a fixed table on which the wafers are mounted, and a movable table which faces the fixed table and can be elevated with a wafer absorbed on its bottom side. The fixed table and the movable table contain their respective heaters. In the bonding apparatus, the two wafers overlap each other and then are bonded together by the pressure created from the weight of the fixed table and the movable table while being heated by the heaters.
However in some instances when two wafers are bonded together, the bonding portions of metal formed on surfaces of the wafers may be bonded together. In this case, there is a need to pressurize the metal bonding portions while heating them to a predetermined high temperature. In other words, there is a need to sequentially perform a pre-heating step of heating the wafers to a predetermined temperature, a bonding step of pressurizing them while maintaining a predetermined temperature, and a post-heating step of cooling them.
However, in the pre-heating step, since the predetermined temperature is high, the use of the prior art bonding apparatus requires time to heat the wafer to the predetermined temperature. In addition, if the wafers are rapidly heated, since the metal boding portions may not be uniformly heated, there is a need to heat the wafer below a predetermined rate of heating. In addition, since the predetermined temperature is high, it takes time to cool the hot wafers in the post-heating step. Further, if the metal bonding portions are alloyed and bonded together, and the wafers are rapidly cooled, since the strength and physical property of the metal bonding portions may be changed, there is a need to cool the wafers below a predetermined rate of cooling. Moreover, the time taken for the bonding step cannot be shortened since it depends on material or the like used in the metal bonding portions.
As such, in the prior art, it is required to adjust the temperature of the wafer for bonding between the wafers having the metal bonding portions. As a result, it takes a long time to bond the wafers. This results in low production yield in the wafer bonding process.